package plan

import (
	"context"
	"fmt"
	"strings"
	"sync"
	"time"

	"go.dagger.io/dagger/compiler"
	"go.dagger.io/dagger/plan/task"
	"go.dagger.io/dagger/plancontext"
	"go.dagger.io/dagger/solver"

	"cuelang.org/go/cue"
	cueflow "cuelang.org/go/tools/flow"

	"github.com/rs/zerolog/log"
	"go.opentelemetry.io/otel"
)

type Runner struct {
	pctx   *plancontext.Context
	target cue.Path
	s      solver.Solver
	tasks  sync.Map
	mirror *compiler.Value
	l      sync.Mutex
}

func NewRunner(pctx *plancontext.Context, target cue.Path, s solver.Solver) *Runner {
	return &Runner{
		pctx:   pctx,
		target: target,
		s:      s,
		mirror: compiler.NewValue(),
	}
}

func (r *Runner) Run(ctx context.Context, src *compiler.Value) error {
	if err := r.update(cue.MakePath(), src); err != nil {
		return err
	}

	flow := cueflow.New(
		&cueflow.Config{
			FindHiddenTasks: true,
		},
		src.Cue(),
		r.taskFunc,
	)

	if err := flow.Run(ctx); err != nil {
		return err
	}

	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
		return nil
	}
}

func (r *Runner) update(p cue.Path, v *compiler.Value) error {
	r.l.Lock()
	defer r.l.Unlock()

	if err := r.mirror.FillPath(p, v); err != nil {
		return err
	}
	r.initTasks()
	return nil
}

func (r *Runner) initTasks() {
	flow := cueflow.New(
		&cueflow.Config{
			FindHiddenTasks: true,
		},
		r.mirror.Cue(),
		noOpRunner,
	)

	// Allow tasks under the target
	for _, t := range flow.Tasks() {
		if cuePathHasPrefix(t.Path(), r.target) {
			r.addTask(t)
		}
	}

	// If an `output` task is targeting an allowed task, allow the output task as well
	for _, t := range flow.Tasks() {
		if t.Path().Selectors()[0] != OutputSelector {
			continue
		}
		for _, dep := range t.Dependencies() {
			if r.shouldRun(dep.Path()) {
				r.addTask(t)
			}
		}
	}
}

func (r *Runner) addTask(t *cueflow.Task) {
	r.tasks.Store(t.Path().String(), struct{}{})

	for _, dep := range t.Dependencies() {
		r.addTask(dep)
	}
}

func (r *Runner) shouldRun(p cue.Path) bool {
	_, ok := r.tasks.Load(p.String())
	return ok
}

func (r *Runner) taskFunc(flowVal cue.Value) (cueflow.Runner, error) {
	v := compiler.Wrap(flowVal)
	handler, err := task.Lookup(v)
	if err != nil {
		// Not a task
		if err == task.ErrNotTask {
			return nil, nil
		}
		return nil, err
	}

	if !r.shouldRun(v.Path()) {
		return nil, nil
	}

	// Wrapper around `task.Run` that handles logging, tracing, etc.
	return cueflow.RunnerFunc(func(t *cueflow.Task) error {
		ctx := t.Context()
		lg := log.Ctx(ctx).With().Str("task", t.Path().String()).Logger()
		ctx = lg.WithContext(ctx)
		ctx, span := otel.Tracer("dagger").Start(ctx, fmt.Sprintf("up: %s", t.Path().String()))
		defer span.End()

		lg.Info().Str("state", string(task.StateComputing)).Msg(string(task.StateComputing))

		// Debug: dump dependencies
		for _, dep := range t.Dependencies() {
			lg.Debug().Str("dependency", dep.Path().String()).Msg("dependency detected")
		}

		start := time.Now()
		result, err := handler.Run(ctx, r.pctx, r.s, compiler.Wrap(t.Value()))
		if err != nil {
			// FIXME: this should use errdefs.IsCanceled(err)
			if strings.Contains(err.Error(), "context canceled") {
				lg.Error().Dur("duration", time.Since(start)).Str("state", string(task.StateCanceled)).Msg(string(task.StateCanceled))
			} else {
				lg.Error().Dur("duration", time.Since(start)).Err(err).Str("state", string(task.StateFailed)).Msg(string(task.StateFailed))
			}
			return fmt.Errorf("%s: %w", t.Path().String(), err)
		}

		lg.Info().Dur("duration", time.Since(start)).Str("state", string(task.StateCompleted)).Msg(string(task.StateCompleted))

		// If the result is not concrete (e.g. empty value), there's nothing to merge.
		if !result.IsConcrete() {
			return nil
		}

		if src, err := result.Source(); err == nil {
			lg.Debug().Str("result", string(src)).Msg("merging task result")
		}

		// Mirror task result and re-scan tasks that should run.
		// FIXME: This yields some structural cycle errors.
		// if err := r.update(t.Path(), result); err != nil {
		// 	return err
		// }

		if err := t.Fill(result.Cue()); err != nil {
			lg.Error().Err(err).Msg("failed to fill task")
			return err
		}

		return nil
	}), nil
}

func cuePathHasPrefix(p cue.Path, prefix cue.Path) bool {
	pathSelectors := p.Selectors()
	prefixSelectors := prefix.Selectors()

	if len(pathSelectors) < len(prefixSelectors) {
		return false
	}

	for i, sel := range prefixSelectors {
		if pathSelectors[i] != sel {
			return false
		}
	}

	return true
}

func noOpRunner(flowVal cue.Value) (cueflow.Runner, error) {
	v := compiler.Wrap(flowVal)
	_, err := task.Lookup(v)
	if err != nil {
		// Not a task
		if err == task.ErrNotTask {
			return nil, nil
		}
		return nil, err
	}

	// Return a no op runner
	return cueflow.RunnerFunc(func(t *cueflow.Task) error {
		return nil
	}), nil
}